Conventionally known thermally removable pressure-sensitive adhesive sheets are composed of a backing and a pressure-sensitive adhesive layer that is provided on the backing and contains an expanding or foaming agent such as thermally expandable microspheres (see Patent Documents 1 to 5).
Thermally removable pressure-sensitive adhesive sheets combine tackiness with peelability after use. Specifically, they are so designed that after they achieve the object of adhering to an adherend, their pressure-sensitive adhesive layer, which contains an expanding or foaming agent such as thermally expandable microspheres, expands or foams when heated, so that the surface of the pressure-sensitive adhesive layer is deformed to have asperities, which reduces the area of adhesion to the adherend and thus reduces the adhesive strength, so that the adherend can be easily separated. Therefore, they are used for a variety of purposes, such as fixation (e.g., temporary fixation) of electronic components or materials therefor during processing thereof and fixation (e.g., temporary fixation) of products during distribution such as transportation or conveyance.
Thermally removable pressure-sensitive adhesive sheets are not used in final products and generally incinerated after they are used during processing, transportation and so on. Therefore, since there has been a concern about the depletion of fossil resources or the increase in carbon dioxide due to combustion of fossil resources, which is a cause of global warming, they are required to be produced using plant-derived alternative materials, which are so-called carbon neutral, so that measures can be taken against that.
In addition, synthetic rubbers and acryl-based pressure-sensitive adhesives have been used as adhesive materials for the thermally removable pressure-sensitive adhesive sheets (for example, Patent Document 6), and at present, no available plant-derived acryl-based pressure-sensitive adhesive has been found.